I am running a high-level, low magic campaign, currently 13th level. When the seas iced over thanks to a Levistus activating an elder relic, the possessed warlock of the party spent some time repurposing the ship to shift into the Astral Plane. (May have been fast-talking me on the explanation, but that's unimportant right now.) Now the party is spamming that planar shift to avoid any obstacles in the Material plane.

How can I prove to the party that they shouldn't be in the Astral plane yet, short of railroading them by dropping an Astral Guardian in their vicinity?

\$\begingroup\$Define "obstacles". I don't know enough about 3.5's particular fantasy setup, but oftentimes in fantasy the material plane casts a shadow on the astral plane (or equivalent). That mountain revered by the annoying tribesmen - it's sentient (and annoyed at you for hurting it's worshippers). That big battle you'd rather avoid - it's been going on so long there are empathic ghosts there now. Those pirates who just showed up - some local (powerful) denizen has been prodding them to attack people for the lulz, to bad you left the easy fight in the other plane...\$\endgroup\$
– Clockwork-MuseFeb 25 '14 at 11:49

\$\begingroup\$Life on a ship can be a nuisance if you have an infinitely long silver cord attached to your body. Keeps getting tangled on the mast and in the rig all the time. Let's hope that doesn't happen in combat...\$\endgroup\$
– DamonFeb 25 '14 at 17:55

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\$\begingroup\$Is your problem that you don't want them in the Astral Plane, or that you've got Material-plane obstacles that you do want them to go through?\$\endgroup\$
– StandbackFeb 25 '14 at 18:40

\$\begingroup\$Additionally: how far in are you? Have you already established any "local" conventions about how astral travel works, or can you still comfortably set up new conventions and expectations?\$\endgroup\$
– StandbackFeb 25 '14 at 18:42

9 Answers
9

Making the Astral Plane a High-level Destination

The Astral Plane is already a mid-level destination. The chart Astral Plane Encounters (DMG 154) lists the minimum Astral Plane encounter as EL 8 with 1 noble djinn (MM 114-5) (perhaps accompanied and captured--so it can grant wishes--by some insignificant-to-the-EL githyanki who lost their mid-level githyanki during their encounter with the djinn) but goes up to EL 14, which might challenge your PCs without consulting other sources.

The Manual of the Planes gives a 1 in 20 chance per hour of a a random encounter on the Astral Plane using Table 5-3: Astral Encounters (53), and those range from easy (a CR 5 solitary nightmare (MM 194)) to extreme (the CR 17 astral form of a Wiz17), but centers on EL 11 encounters. Essentially, that means at least once per day, the PCs will encounter something, and it's liable to be ready for a fight (or running from one), and some lousy days on the Astral Plane it's liable to be an encounter traffic jam.

What this also means is that your PCs are leveled appropriately to start adventuring on the Astral Plane. I understand you not wanting them there, but the game thinks it's okay that they are.

Increasing the basic lethality of the Astral Plane is seriously the easiest way to make the players think again about visiting, but you could place a plot hook there so terrifying the PCs can't even imagine dealing with it--a cult of mind flayers attempting to bring back to life a dead god, for example--then say offhandedly, "Yeah, that's for when you hit epic levels."

There Might Be Confusion about Traveling the Astral Plane

The D&D Cosmology says, "All planes... are coexistent with the Astral Plane" (DMG 150), but the Astral Plane lacks the overlap with the Prime Material Plane possessed by, for example, the Ethereal Plane or the Plane of Shadow. Instead the Astral Plane "envelops the whole cosmology like a cloud." A ship or creature on the Astral Plane doesn't have correspondence to any location on the Prime Material Plane; there's just no relationship there.

To clarify, when the ship travels to the Astral Plane, the ship arrives at a destination that's only and ever on the Astral Plane. When the ship returns to Prime Material Plane, the PCs pick a destination at which the ship will arrive, and poof! the ship appears there (although possibly 5d% miles off-target if the repurposing incorporated an effect like the spell plane shift [conj] (PH 262) and you interpret the spell that way). That effect is like a high-volume, time-consuming (two standard actions!), and maybe more accurate version of the spell teleport [conj] (PH 292-3). In a more magic-intensive game, the PCs could've been doing that at least 4 levels ago, albeit on a more limited scale.

Further, if the ship's generating an effect like the spell plane shift [conj] (PH 262), then the ship should arrive 5d% miles from the chosen destination on the Astral Plane, which might not matter if the PCs are just using the Astral Plane as an escape route but does mean every time the ship arrives on the Astral Plane it's in a different place, possibly with new, unknown threats.

Slowing the Ship
Foes tired of the PCs escaping to the Astral Plane can discover their Astral Plane destination with the feat Astral Tracking (Dragon Compendium Volume 1 92) and, once they arrive at that destination, cast on the site the spell hallow [evoc] (PH 238), tying to the site an effect like the spell dimensional anchor [abjur] (PH 221).

Then, to reach a different Astral Plane destination beyond whatever the ship's now-blocked default, the PCs must either learn of another Astral Plane location via research (the resources for which you needn't provide until you're ready for this to be a thing again) or discover that location via exploration, which entails entering the Astral Plane by other means and scooting around until something presents itself.

Also, so you know, if the ship's prevented from returning to the Prime Material Plane, the PCs should quickly learn that "[o]bjects... cannot move in the Astral Plane, though they may be pushed" (MP 47); that might make the crew unhappy. (The 3.5 DMG says the Astral Plane has subjective directional gravity (154) meaning the Astral Plane has "no gravity for unattended objects" (148)--the upper limit of what objects can be attended is up to the DM.) This might mean PCs traveling bodily in the Astral Plane, navigating its hazards and encounters, to reach help sufficient to push their ship, but that A) is an adventure! and B) likely requires abandoning their ship. So you know, only "githyanki possess special item creation feats that enable them to create their famed astral ships" (MP 52). Let hilarity ensue.

A Final Concern
Although the githyanki have astral ships (see above), they are "difficult to create, requiring years of work" (MP 52), and the spell that does what your level 13 characters are doing is similar to the 9th-level Sor/Wiz spell planar navigation [conj] (Sto 119-20) (although that spell transports the ship to a body of water on any plane instead of just to the Astral Plane). I mention this because based on the precedent set by that spell your PCs are doing something similar at least 4 levels early (barring shenanigans) than the game expects, even if it is via a magic item (i.e. their repurposed ship). It might not seem like a lot, but 4 levels is the most extreme difference between a challenging encounter and a very difficult encounter (DMG 49). It appears too late to introduce a wrinkle into the repurposing process that makes their traveling to the Astral Plane expensive, limted, time-consuming, or unreliable, but you might discuss these nuts-and-bolts issues with your group.

\$\begingroup\$Excellent, thorough look at where the situation stands in relation to expected power levels. Kudos.\$\endgroup\$
– StandbackFeb 25 '14 at 18:46

\$\begingroup\$On the "confusion about travelling the Astral" bit, it might be worth adding that in earlier editions, the astral plane didn't have the concept of distance as it is understood on other planes. There, the distance between two landmarks is more akin to the distance between one idea and the next: As long or short as you can conceptualise it to be. Literally. As in, intelligent characters travel faster because they can more rapidly reason their way to the conclusion (of their journey).\$\endgroup\$
– GMJoeFeb 27 '14 at 4:10

They want to be on the astral plane? Fine. Just give them astral obstacles. Or better, opponents who can track them from plane to plane.
You can also use some kind of dimensional anchor, but again, I would advice not to use it to stick them on the material plane. Instead, let them go to the astral plane, place any very dangerous obstacle (use your imagination: a war between god-like beings with the PCs in the middle, for example), and anchor them there. Make them want to be on the material plane. ;-) Moreover, after that, make sure they will think about it twice before transplaning. Do not forbid them to do so, just make it so perilous that they should do it only if it's worth the danger.

You've got a few options for forcibly removing a party from the astral, which are largely the same as convincing them to avoid it until they're higher level but don't overlap entirely.

Show them the natives
While making them fight an Astral Guardian, or Astral Dreadnought, or Githyanki raiding party may or may not be railroading depending on setup, you don't actually need to make them fight anything. Simply showing them to the players, possibly fighting each other to give an indication of scale or power, may be enough to convince them to keep to safer waters for the time being.

Spells
Spells can remove the party from the Astral, if a combat encounter is desired. Dismissal was suggested in GMJoe's answer, though it suffers from being single target. Banishment is a higher level version of the same spell, that affects multiple creatures (up to 2HD per caster level), but seems unlikely to successfully target the entire party. Removing a party member or two might scare them into fleeing, whether the entire party is forcibly removed or not. These spells do not indicate where in their home plane a creature is sent to, but do include a random 20% chance of the targets being sent to a different plane. Recovering party members from a random location might be difficult, time consuming, dangerous, or all of the above.

Holy Word and blasphemy will also banish the entire party on a failed save (assuming they are either non-good or non-evil, respectively). These spells further preclude those banished from returning for 24 hours. These are probably your best bets for simple party removal, and should be available to a level 13 cleric, though they come with some unpleasant side effects.

Plane Shift can also be used offensively, as it can be used as a standard action touch attack that grants a will save. This is less effective than dismissal, however, but allows for the target to be removed from the plane and sent someone other than their plane of origin. Like some place very unpleasant.

Environmental Hazards
There are also environmental hazards you could use to convince them that the plane isn't a great place to visit without reason. While the 3.5e Planar Handbook has no such hazards in it that I can find, the 3.0 Manual of the Planes includes a description of Psychic Storms on page 51. These generally blow you off course and disrupt your travel, including sending you through a random color portal to a different planar destination. While that will remove the party from the plane, they could just counter this with another ship-wide plane shift and only lose some time.

As a last resort, you could adapt the 2e rules on Psychic Winds found in the Planescape Guide to the Astral Plane, page 40. These included other storms like Emotional Tempests (loss or gain of 1 or more emotions for a time) and Dreamstorms (confusion, fear, general penalties, and possible permanent phobia). These are largely roleplaying inconveniences, however, and it's unclear whether your group would be sufficiently annoyed by them to avoid the astral. It could pair well with being blown out of the Astral, however, if they are ejected and unable to return for a time because of complications from these effects.

\$\begingroup\$You could always associate a power source and/or charges to the ship as well.\$\endgroup\$
– SquishFeb 25 '14 at 15:54

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\$\begingroup\$While true, that potentially retcons things a bit and I don't really like suggesting that without the broader table discussion that should accompany a retcon. And if you're going to have a broader table discussion about the implications of astral shifting around obstacles (which sounds more like etherealness in general, but I digress), you can just handle the whole problem there as well by reaching consensus. I actually think that's a better solution to the underlying problem than trying to use mechanics to dissuade the characters, but that wasn't what the question was asking for.\$\endgroup\$
– tarkisfluxFeb 25 '14 at 19:33

Unfortunately, now the party is spamming that planar shift to avoid
any obstacles in the Material plane.

There is an extremely easy way to make them stay on the Material plane -- give them something to do on the Material plane. Goals, jobs, enemies -- enemies that they wish to defeat, not avoid. Play on their backstories, on their character desires, on their goals and methods.

Unless their very only desire is to survive, this should give them enough incentive to stay. Sure, they can planeshift away and leave that dungeon alone, but nobody is going to stop the villain while they are away. The world won't wait while they are away chatting up the githzerai. It will move, and it will kill, it will destroy and it will defile what they hold dear. Unless, of course, they stop planeshifting from everything, and fight back.

Your campaign is transitioning power levels, and you need to adjust. Just as cliffs aren't an obstacle once a party has Fly, nothing physical is an obstacle once a party has teleport and, later, Dimension Shift.

You've been able to railroad them using physical obstacles to this point. Now if you want them to follow your plot, you need to use plot obstacles. How is it that Lex Luthor always manages to get Superman where he needs him? It surely isn't by building a big wall. How does work get you to show up? Not by forcing your car to follow a certain route...

So come up with creative solutions that challenge their new capabilities, rather than simply denying them use of those capabilities. They keep shifting away? Well, that leaves a trail. Maybe someone wants a ride. Maybe there's astral weather. Maybe while they're away, bad things happen to people or things they care about.

The old methods won't work, so you need to shift your thinking--this is one of the fun things about being a GM!

Assuming none of your party is native to the Astral, you could just have some angry githyanki dismiss them; Being hurled to a random location on your home plane is a potentially awesome setup for an adventure and is almost certainly going to be a major setback to their travel plans.

\$\begingroup\$oh dear. Dismissal is single target. So they disappear one by one as they fail their saves...\$\endgroup\$
– Brian Ballsun-StantonFeb 25 '14 at 5:31

2

\$\begingroup\$As a followup adventure, you could have the players trying to win their ship back from the Githyanki, who are using it to mount raids on the Prime...\$\endgroup\$
– GMJoeFeb 25 '14 at 5:33

\$\begingroup\$Is there meta-magic available to make dismiss multi-target?\$\endgroup\$
– doppelgreener♦Feb 25 '14 at 5:37

2

\$\begingroup\$@JonathanHobbs Not that I know of, but surely some enterprising gish has researched a mass dismissal spell by now. That said, it's not really necessary to make it multi-target, is it? Just have multiple castings and casters, possibly due to a staff or other magical item; You'll need those to guarantee all the PCs fail their saves anyway.\$\endgroup\$
– GMJoeFeb 25 '14 at 5:40

6

\$\begingroup\$It's called Banishment And should be accompanied by a bound copy of the grapple rules to increase the DC versus the PCs. See also Githyanki Dismissal (cPsi).\$\endgroup\$
– Brian Ballsun-StantonFeb 25 '14 at 10:14

Instead of coming up with mechanics that will throw them back to the physical plane or prevent them from entering the astral plane and possibly frustrating your players because they feel you are "trying to prevent them from having fun", I suggest simply talking with them.

Explain that their abuse of phase shifting makes it difficult for you to come up with meaningful campaigns that do not involve them skipping straight to the end. This has the desired effect, without the possibility of offending players who think you are "trying to ruin their fun".

Unbeknownst to the party, the ship has always had charges. It just ran out of them.

Astral termites infest the ship. Each trip, 1d4 passengers must make Reflex saves or be injured as parts of it break unexpectedly. Repairing the ship causes it to lose its magical properties.

Magical fungus starts growing inside hull, spores require Fortitude saves daily from all characters or lose 1 point of constitution. Fire will kill the fungus but may burn the ship, too - too bad there's not actually any water on the astral plane!

The party have some treasure, other magic item, person or macguffin that, for whatever reason, cannot be brought to the Astral Plane. Perhaps doing so will attract the attention of demonic nasties, or the person/thing in question is a bound form of a demonic nasty that can escape if let off the astral plane (bonus points if you don't tell them that beforehand...) Maybe something is too sensitive to magic to survive there, or not sensitive enough to be transported in the first place, etc.

Before you can convince them of this, you need to have your own answer. Why shouldn't they be on the Astral Plane yet? If you can't answer this without going into metagame terms, then maybe there really isn't a reason they shouldn't be there.

Most Material Plane obstacles can be translated, one way or another, into planar obstacles. If they want to circumvent your Material Plane obstacles, that's fine: what awaits them on other planes can be just as difficult to overcome, but weirder. Ideally, they could be so weird that the players never even notice that mechanically, these are exactly the same things they'd be doing if they went through the Material Plane.

Obstacles provided by humanoids are the easiest to translate, due to the githyanki. Bandits, for example, become githyanki pirates or slavers. Non-humanoids are tougher, but far from impossible: there's no need to throw a Dreadnought into their path. Natural obstacles get a little trickier, but you also don't have to use the Astral Plane for them: open up color pools with decently-high DCs to avoid them, and sooner or letter you'll hurl them much further off-course than they'd intended to go, to planes where you can do more in the way of obstacles than ever before.

The bottom line is that you probably can't force them back onto the Material Plane, but you also don't have to. They want to explore the planes? Fine. Let's explore the planes. Just make sure they aren't featureless, obstacle-free paths to the goal, and you'll get the sorts of challenges you were hoping for. They might look different, but it doesn't have to go any further than that.